1. Field of the Invention
The present invention relates to a device for estimating a drift amount of a lateral acceleration sensor, a device for correcting output of a lateral acceleration sensor, and a device for estimating a road surface friction state, and in particular, to a device for estimating a drift amount of a lateral acceleration sensor which estimates the drift amount of a lateral acceleration sensor without using the difference in wheel speeds between the left and right wheels, and to a device for correcting output of a lateral acceleration sensor which corrects lateral acceleration in accordance with the drift amount, and to a device for estimating a road surface friction state which estimates a road surface friction state by using the corrected lateral acceleration.
2. Description of the Related Art
Conventionally, techniques have been disclosed for estimating the drift amount of a lateral acceleration sensor and correcting the output of the lateral acceleration sensor on the basis of the drift amount (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 9-5352, 11-281672). In the techniques disclosed in JP-A Nos. 9-5352 and 11-281672, the drift amount of a lateral acceleration sensor is detected on the basis of a signal of the lateral acceleration sensor and the difference in wheel speeds of the left and the right wheels.
Concretely, in the technique disclosed in JP-A No. 9-5352, at times which do not correspond to any of a time of acceleration or deceleration, a time of a vehicle spin, a time of high lateral acceleration, and a time of stopping, a lateral acceleration value, which is computed from the difference in wheel speeds of the left and right wheels, and a value of a lateral acceleration sensor are compared, and the drift amount of the lateral acceleration sensor is estimated.
Moreover, in the technique disclosed in JP-A No. 11-281672, the rotational speed of each wheel, and the longitudinal acceleration and the lateral acceleration are detected. By using these results of detection, it is judged whether the vehicle is traveling steadily (i.e., traveling straight ahead at a constant speed on a flat road). The output of the lateral acceleration sensor at the time of steady traveling is detected as the drift amount.
The techniques disclosed in JP-A Nos. 9-5352 and 11-281672 utilize the fact that, when the vehicle is in a state of traveling straight ahead in which the difference in the wheel speeds of the left and right wheels is zero, the lateral acceleration is zero.
However, the difference in the wheel speeds of the left and right wheels is a property which is affected and easily changed by the air pressure of the tires. Therefore, in a case in which, for example, both of the front and rear tires at one of the left and right sides have been punctured, or the like, a difference in wheel speeds between the left and right wheels will arise even if the vehicle is traveling straight forward. A problem will arise in that the drift amount will be estimated incorrectly.